The present invention relates to a signal reproduction block in a disk apparatus such as a DVD reproduction apparatus for reproducing a signal of data read out from a disk such as an optical disk and more particularly to a technique for avoiding an adverse influence of an output signal line on a data signal reproduction process in a case where the output signal line is additionally provided for a characteristic information signal representing a characteristic of a filter that is incorporated in the signal reproduction block.
Typically, in a circuit chip in which a low pass filter (hereinafter referred to as an xe2x80x9cLPFxe2x80x9d) is incorporated, an input signal is input to a variable gain amplifier 51 (hereinafter referred to as a xe2x80x9cVGAxe2x80x9d) via a signal line 501, and the signal is subjected to gain adjustment in the VGA 51, after which it is input to an LPF 52 via a signal line 502, as illustrated in FIG. 7. During a filter characteristic measurement process, a characteristic information signal, which is obtained by inputting a test signal to the LPF 52, is input to a buffer 61 via a signal line 601, and the drivability thereof is increased through the buffer 61, after which the characteristic information signal is taken to the outside of the circuit chip via a signal line 602. Then, outside the circuit chip, a characteristic of the LPF 52 such as the gain, the phase or the group delay is measured by using a measuring apparatus.
An example in which a filter is incorporated as described above is a signal reproduction block in a disk apparatus such as a DVD reproduction apparatus for reading out data written on a disk so as to reproduce a signal of the data.
The signal reproduction block operates as follows during a signal reproduction process. Referring to FIG. 8, an analog signal of data read out from the disk is amplified by a pre-amplifier, and then input to the VGA 51 via the signal line 501 for gain adjustment, after which the signal is input to the LPF 52 via the signal line 502 for waveform equalization. The output signal from the LPF 52 is passed to an A/D converter 53 via a signal line 503 so as to be converted to a digital signal, which is then passed to a digital signal processing section 54 via a signal line 504, where the signal is reproduced by digital processing. Then, the signal is output to a controller (not shown) in the following stage via a signal line 505.
The signal reproduction block described above may be provided with the function of outputting a filter characteristic information signal as that of the circuit chip described above by providing the output signal line 601 for taking out the characteristic information signal representing a characteristic of the LPF 52 so that the output signal line 601 diverges from the signal line 503 between the LPF 52 and the A/D converter 53, with the buffer 61 being provided along the output signal line 601, as illustrated in FIG. 8 in the area delimited by a phantom line.
In the signal reproduction block, however, a parasitic effect occurs due to the presence of the output signal line 601. Then, during the process of reproducing a data signal, the signal along the data signal path for performing the signal reproduction process may be deteriorated, thus adversely influencing the reproduction process.
An object of the present invention is to make it possible to ensure reliable reproduction of a data signal by suppressing the deterioration of the data signal due to a parasitic effect of an output signal line additionally provided for a filter characteristic information signal during the data signal reproduction process, in a case where a signal reproduction block of a disk apparatus such as a DVD reproduction apparatus is provided with a function of outputting a characteristic information signal during a filter characteristic measurement process.
In view of the fact that a signal along the data signal path for performing a signal reproduction process is an analog signal between the filter and an A/D converter but is a digital signal on the output side of the A/D converter, the present invention provides an output signal line for outputting the filter characteristic information signal to the outside on the output side of the A/D converter, whereby when a data signal is reproduced the signal is prevented from deteriorating due to the parasitic effect of the output signal line.
Specifically the present invention provides a signal reproduction block, including: a filter for waveform equalization of an analog input signal; an A/D converter for converting an output signal from the filter to a digital signal; a digital signal processing section for reproducing an output signal from the A/D converter; and an output signal line through which a characteristic information signal that is obtained by inputting a test signal to the filter is output to an outside of the signal reproduction block during a characteristic measurement process of measuring a characteristic of the filter, wherein the output signal line is provided on an output side of the A/D converter.
With such a configuration, when reproducing a data signal, the data signal read out from a disk is still an analog signal after the signal passes through the filter, but is a digital signal on the output side of the A/D converter. Since the output signal line for outputting the characteristic information signal to the outside of the signal reproduction block during the filter characteristic measurement process is located on the output side of the A/D converter, it is possible to prevent the signal from being deteriorated during the signal reproduction process due to a parasitic effect of the output signal line.
Moreover, since the characteristic information signal is output after it is converted to a digital signal by the A/D converter, the deterioration thereof is reduced as compared with a case where the characteristic information signal is output as an analog signal thus improving the measurement precision accordingly. Note that xe2x80x9cfilter characteristicxe2x80x9d as used herein is not limited to the group delay characteristic which is discussed in detail below in the description of the embodiments of the invention, but may alternatively be other characteristics such as the gain characteristic or the phase characteristic.
In one embodiment of the invention, an input signal to the filter is a differential signal the signal reproduction block further including: a bypass signal line for taking out an unfiltered signal to be input to the filter; and a signal selection circuit for receiving the unfiltered signal taken out by the bypass signal line and a filtered signal output from the filter, and for simultaneously outputting the unfiltered signal and the filtered signal to the A/D converter during the characteristic measurement process while outputting only the filtered signal to the A/D converter during a signal reproduction process.
With such a configuration, two signals, i.e., the unfiltered signal and the filtered signal, are A/D-converted simultaneously during the characteristic measurement process. Moreover, during the signal reproduction process, only the filtered signal is input to the A/D converter by the signal selection circuit, whereby the signal reproduction process is not hindered. Note that since the bypass signal line is arranged within the analog circuit and has a small path length the deterioration of the data signal due to the parasitic effect of the bypass signal line is practically negligible as compared with a case where the output signal line is extended to the outside of the signal reproduction block diverging from a signal line on the output side of the filter (see FIG. 8).
In one embodiment of the invention, the signal reproduction block further includes a calculation section provided on the output signal line for calculating and outputting a time difference between the unfiltered signal and the filtered signal, which have been converted to digital signals by the A/D converter. With such a configuration, the delay characteristic of the filter is obtained.
In one embodiment of the invention, the test signal is a signal of a single frequency. Note that there may be only one type of test signal, or there may be a plurality of test signals of different frequencies. With such a configuration, measurement with a high precision can be easily performed, as compared with a case where test signals have a plurality of frequencies.
In one embodiment of the invention, the signal reproduction block further includes a test signal generation circuit for generating the test signal. With such a configuration, it is no longer necessary to provide a test signal generation circuit that is external to the signal reproduction block.
In one embodiment of the invention, the test signal generation circuit is configured so as to generate a plurality of test signals of different frequencies. With such a configuration, it is possible to measure the filter characteristic for each of the frequencies of test signals generated by the test signal generation circuit.
In one embodiment of the invention, the test signal generation circuit includes: a basic signal generation circuit for generating a basic signal of a single frequency; and a signal conversion circuit for converting the basic signal generated by the basic signal generation circuit to a plurality of test signals of different frequencies. With such a configuration, the function of the test signal generation circuit is specifically implemented.
In one embodiment of the invention, the signal reproduction block further includes a clock circuit for generating a clock signal, wherein the basic signal generation circuit of the test signal generation circuit is the clock circuit. With such a configuration, it is possible to provide the basic signal generation circuit without increasing the circuit area.
In one embodiment of the invention, the signal conversion circuit of the test signal generation circuit is provided outside the signal reproduction block. With such a configuration, the adjustment of test signals according to the measurement conditions can be performed easily, as compared with a case where the signal conversion circuit is provided within the signal reproduction block.